What is the harm caused by the ultra-low loaded operation of boiler?

The load control is quite significant in boiler's operation. Both overloaded and ultra-low loaded operations have negative effects on boiler. Different types of boiler have different rated load ranges, but ultra-low loaded operation's harm to different types of boiler is similar.

In general, the normal load change range of coal-fired boiler is 70%-100% of the rated load and that of gas-fired/oil-fired boiler is 60%-100% of the rated load. If boiler runs with the load lower than this range, it means that the boiler is in ultra-low loaded operation.

Ultra-low loaded operation can give rise to the instability of boiler combustion. The bed temperature can be easy to fluctuate and difficult to be adjusted. It can even result in flame-out. All of these affect boiler's normal operation. When boiler is in long-term ultra-low loaded operation, the imbalance between coal feeding quantity and ash returning quantity can cause the uneven heating of heat exchange tubes, which can greatly reduce the service life of boiler's internal tubes.

Ultra-low loaded operation can also lower boiler's exhaust gas temperature and then increase the probability of corrosion of heat exchange tubes at the end of boiler. Meanwhile, furnace temperature can also be lowered to cause problems such as incomplete combustion and low production efficiency.

For gas-fired boiler, it originally adopts natural water circulating method. When it is in ultra-low loaded operation, the flow velocity of water circulation is lowered and the reliability of water circulation is also lowered due to less fuel feed.

It is more important that boiler in the ultra-low loaded operation can not ensure the steam quality because the steam temperature of boiler outlet is lower and is difficult to maintain, which can cause worse and worse steam that can not meet the actual demands.